This research focuses on the effects on the infant of mother loss in the Indian langur monkey (Presbytis entellus). Langur monkeys have multiple important caretakers from the day of birth and a one day old infant may be passed from one female to another as many as 80 times in four hours. This is the normal langur monkey pattern and makes them valuable subjects for the investigation of the reactions following loss of mother. Results will be compared with separation studies of macaques where the primary and usually exclusive caretaker is the mother, and for which mother loss can have devastating effects. By removing the mother for two weeks, and then reuniting the mother and infant, this study aims to provide new insights into the spectrum of potential responses to loss in monkeys and to provide specific data on how an infant's reactions to mother loss integrated within a multiple caretaker naturational setting can have an adaptive outcome of infant survival. Other factors important in the study include the infant's early experiences with caretakers, sibs, and peers, and the adequacy of available substitute mothering. All infants are observed from the day of birth using a focal animal sampling technique to maintain a continuous data base against which experimentally produced behavior is evaluated.